In the practice of keyless inking for lithographic printing whereby ink is metered into the printed system by means of a metering roller and a cooperating scraping blade, Fadner in U.S. Pat. No. 4,601,242, Fadner and Hycner in U.S. Pat. No. 4,537,127 and Fadner in U.S. Pat. No. 4,603,634 have disclosed advantageous method and means wherein the surface of an ink metering roller will possess the dual property of being both hydrophobic and oleophilic, that is water-repelling and oil attracting. This dual property can be present whether the lithographic ink metering roller surface is formed with ink retaining dimensioned cells or is formed with a surface possessing irregularly spaced cavities capable of retaining ink. In practicing keyless inking the presence of oleophilic and hydrophobic properties at the surface of the ink metering roller is vital, since lithography requires the presence of water in the films of ink being used. The presence of hydrophilic, or water attracting regions on the ink metering roller surface will allow water to displace or debond ink from those regions, thereby disrupting the roller's ink carrying and ink metering capabilities.
The above-named Fadner, et al, prior art references also teach that even when consistent ink metering is assured by providing a metering roller surface that is both hydrophobic and oleophilic, the water contents of the ink films on the inking rollers may vary across the press width, depending upon the relative amounts of ink and water consumed in satisfying the format being printed. To accomplish uniform ink availability across the press during a printing run, it is necessary to assure that a constant ink composition is continuously available to all portions of the printing plate. Unless constant ink composition is available across the press width, the water content tends to increase in regions of low print density and undesirable print quality occurs. Means for obtaining press wide uniformity of ink composition are disclosed in the Fadner, et al U.S. Pat. No. 4,690,055.
When hydrophilic regions are purposefully included in either a random or in geometrically uniform manner, such as the land areas of the celled metering roller disclosed in U.S. Pat. No. 4,637,310 by Sato and Harada or as in the non-celled or smooth-surfaced metering roller disclosed in U.S. Pat. No. 4,287,827 by Warner, it might be reasoned that predictability of ink metering will be achieved because any water interference due to debonding of ink from the hydrophilic regions would be in accord with the pattern selected when forming the hydrophilic regions. However, the through-puts of water and ink across the press width and therefore the relative amounts of each required, are determined by the image and non-image format on the printing plate being used at any given time. Printing formats are not uniform generally and are rarely the same from press-run to press-run. Consequently, the extent of ink debonding by water when operating an apparatus utilizing the oleophilic and hydrophilic technology will depend upon the instantaneous amounts of water present in the ink at various locations on the metering roller. These locations correspond in turn to the various cross-press ink and water amounts required to print the format on the printing plate. The higher the water content in the ink at a hydrophilic/region, the greater will be the propensity for loss of ink carrying capability because of debonding of ink in the corresponding localized region. The result is variable ink input from press-run to press-run as the printed format is changed, with concomitant printed regions of unexpectedly low or unexpectedly high optical density.
Hard ceramic materials, such as chromium and aluminum oxides and tungsten carbide are naturally high energy materials and correspondingly tend to be hydrophilic in the presence of water and tend to be oleophilic in the presence only of oily materials. Metering rollers manufactured using these materials, while often used successfully in conjunction with either water based inks or with oil based inks in letterpress printing, fail to deliver consistent quantities of ink during lithographic printing utilizing oil-based inks having water present. The extent of ink delivery inconsistency is determined by whether water present in the ink has displaced or debonded ink from the roller's ceramic surface. As previously noted, the extent of debonding depends upon the water content of the ink at any selected cross-press location, which water content in turn depends upon the format being printed.
The previously referred to Fadner U.S. Pat. No. 4,601,242 discloses one means to use the advantageously hard and wear-resistant ceramic property to obtain reasonably long lithographic ink metering roller lifetimes. Specifically, ceramic powder, and in particular alumina, is flame sprayed in a purposefully thin layer of less than about 2 mils thickness over a copper-plated metering roller base. Copper is naturally hydrophobic and oleophilic. This procedure results in a hard, wear-resistant surface that has sufficient inter-particle porosity relative to ink and water interactions that the surface acts as if it was copper, therefore retaining ink in preference to water, yet simultaneously acts as a wear-resistant ceramic material relative to scraping blade wearing action. Although commercially viable, this type of roll has a lifetime on a printing press of about 20 to 30 million printing impressions, because the ceramic layer must be kept relatively thin to assure that the oleophilic property of the underlying copper is not negated by the hydrophilic properties exhibited by the ceramic layer. Further, the ceramic layer, which is naturally hydrophilic, may become increasing hydrophilic due to accumulation of contaminants associated with use and cleaning of printing presses.
A primary object of this invention is to provide a simple, inexpensive ink metering roller that ensures long operational lifetimes in keyless lithographic printing press systems where the presence of water in the ink is involved.
An additional object of this invention is to provide a process for producing an ink metering roll having a microporous wear-resistant surface layer that is infused with a chemically inert substantially organic material that is oleophilic and hydrophobic.
Still another object of this invention is to provide means whereby hard and wear-resistant but naturally hydrophilic ceramic materials can be used as part of a composite layer that has hydrophobic and oleophilic properties without detracting from their naturally excellent wear-resistant quality.
A further object of this invention is to provide an improved inking roller having a composite structure that combines high degrees of wear resistance with a preferential attraction for and retention of oil inks in the presence of water.
Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawing in which: